This invention relates to cathode ray tubes (CRTs), and more particularly to an assembly for replaceably mounting a getter inside a CRT.
A color cathode ray tube (CRT), has an electron gun mount assembly for forming and directing three electron beams to a luminescent screen containing phosphor deposits located on a glass faceplate panel. A shadow mask frame assembly (or otherwise known as a color selection electrode) comprising either a formed mask or a tension mask, is located between the electron gun mount assembly and the screen. The electron beams emitted from the electron gun mount assembly pass through apertures in the shadow mask and strike the screen causing the phosphor deposits to emit light so that an image is displayed on a viewing surface of the faceplate panel. An internal magnetic shield (IMS) is fastened to the shadow mask frame to reduce the influence of ambient magnetic fields on the electron beam trajectories.
The CRT operates within a vacuum maintained within a sealed envelope. The envelope is evacuated and sealed during the manufacture of the CRT. Because the vacuum can degrade over the life of the CRT by the outgassing of various components sealed inside the envelope, a getter is placed inside the envelope during manufacture to prevent degradation of the vacuum. The getter typically contains primarily barium compounds in a getter cup that are flashed or vaporized after the envelope is sealed by placing a RF coil near the outside of the CRT funnel adjacent the getter. The RF energy from the activated coil vaporizes the getter material and deposits the getter material on surfaces within the envelope. The vaporized getter material absorbs and reacts with residual gas molecules in the CRT, removes the molecules, and continues to absorb any further liberated gases throughout the life of the CRT.
A getter assembly, which includes the getter attached to a getter spring, is often attached to the top or anode cup of the electron gun mount assembly. The getter is positioned out of the yoke region to minimize any interference of the getter with the magnetic field generated by the yoke. This getter assembly configuration is referred to as an antenna getter spring assembly. This configuration is particularly applicable to CRTs having deflection yokes that operate at relatively slow rates (1H). In CRT""s employing higher scan-rate yokes (2H or higher), it is more desirable to have the getter spring assembly positioned even further away from the yoke because the getter assembly has a greater tendency to distort the magnetic field of the yoke in higher scan-rate yokes. Consequently, some CRT manufacturers place the getter further toward the screen in the CRT envelope. In these cases, the getter is attached to the shadow mask frame or the exterior side of the IMS.
In the CRT industry, it has been found necessary from time-to-time to replace the electron gun mount assembly in finished CRTs wherein the getters have already been flashed. CRT""s with replaced mount assemblies are referred to as re-necked tubes. When antenna getter spring assemblies cannot be utilized (e.g., in systems with high scan-rate yokes) a replacement getter spring assembly may not be readily replaced and attached to the mask or IMS in an open envelope.
It is therefore desirable to develop a getter assembly wherein the getter may be easily replaced within the CRT, yet remain stationary for the life of the CRT. Such a replaceable getter assembly would decrease manufacturing costs and increase manufacturing efficiency for re-necked tubes.
This invention relates to a cathode ray tube (CRT) having a replaceable getter attachment assembly for removeably securing a getter within the CRT. The CRT includes a funnel sealed at one end to a faceplate panel with a luminescent screen on an inside surface thereof, a color selection electrode assembly disposed within said envelope and in proximity to said screen, and an internal magnetic shield (IMS) secured to the color selection electrode assembly. The getter attachment assembly includes a mounting rail and a replaceable getter portion. The mounting rail comprises a first portion having a coupling clip for attaching the mounting rail to the internal magnetic shield and a second portion extending therefrom. The replaceable getter portion is detachably attached to the second portion of the mounting rail and extends from the mounting rail to a distal end to which a getter is attached for depositing a film of evaporated getter material within the envelope.